This invention relates to an initially flexible cast material that hardens in the presence of water into a semi-rigid state capable of maintaining a body part, such as an arm or leg, in an orthopedically suitable, stable, treatment orientation while permitting a medically appropriate degree of movement to the cast and enclosed body part.
Conventional moisture-curable bandages incorporate substrates impregnated with plaster-of-paris or formed from flexible fiberglass fabric layers impregnated with a moisture-curable resin. Bandages formed from these materials possess several disadvantages. In particular, casts formed using plaster-of-paris bandages have a relatively low strength to weight ratio. This results in a finished cast that is very heavy and bulky. Furthermore, plaster-of-paris splints are slow to harden, requiring 24 to 72 hours to reach maximum strength. Because plaster-of-paris breaks down in water, bathing and showering are difficult. Even if wetting due to these causes can be avoided, perspiration over an extended period of time can break down the plaster-of-paris and create a significant problem with odor and itching.
Although medical bandages utilizing moisture-curable substrates formed from fiberglass fabric layers are lighter, waterproof and permeable to X-rays, cured casts made using such bandages can become brittle, break down during wear and often need to be replaced. Furthermore, fiberglass is a composition that is highly irritating to mammalian skin. When fiberglass casts are removed, irritating dust or fibers are often generated and become embedded in the skin of the patient.
This invention overcomes the disadvantages of prior art fiberglass substrates by providing a medical bandage formed from a resin-impregnated substrate formed from a knitted fabric that incorporates low modulus, inelastic and elastic fibers. The unique substrate of the present invention results in a bandage that exhibits good conformability compared to prior art fiberglass substrates, possesses sufficient rigidity when cured, and shows no loss of strength compared to casts formed from fiberglass substrates. This novel substrate is less brittle and more durable than prior art fiberglass substrates when cured, and does not disintegrate into irritating dust and/or fibers when removed from the injured body part of a patient.
The material is preferably in the form of an elongate knitted tape that is wrapped around the injured limb or other body part while flexible, and that cures in several minutes to the required degree of rigidity. The term “soft” is used only as a term of degree to distinguish it from known cast tapes that are expressly designed to cure to a very rigid state. The invention described below is designed to cure to a less than fully rigid state, and the term “soft” describes this product in comparison to cast tapes that are designed to cure to a very rigid state.
The invention disclosed and claimed in the invention includes a cast tape that incorporates a fiberglass free fabric knitted from high tenacity polypropylene and polyester yarns. The tape is therefore radiolucent, thus requiring less cast removals during treatment.
As described below, the degree of residual flexibility that imparts the comparatively “soft” characteristics is quantified by the term “Immobilization Value”, or “IV.”
Prior art soft cast tapes include fiberglass medical bandages disclosed in U.S. Pat. Nos. 4,968,542; 4,893,617; and 5,007,418. These patents disclose fiberglass cast tape having an Immobilization Value of between 45-50 and 400 pounds.